Introduction
Ada-95 dla programistów C/C++
Dariusz Wawrzyniak
(na podst. oprac. Simona Johnstona)
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
Part I
Ada Basics
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
Outline
1
First View
2
Ada Types
3
Ada Statements
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
First View — outline
1
First View
2
Ada Types
3
Ada Statements
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
First View
Ada is case insensitive, so begin BEGIN Begin are all
the same.
The tick (’) is used to access attributes for an object.
a : Integer := Integer’Size;
In C: int a = sizeof(int) * 8;
Another use for the tick is to access the attributes First
and Last (for an integer the range of possible values is
Integer’First to Integer’Last).
The tick is also used for other Ada constructs as well as
attributes.
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
Operators in C and Ada (1)
Operator
Assignment
Equality
NonEquality
Plus Equals
Subtract Equals
Multiply Equals
Division Equals
Or Equals
And Equals
C/C++
=
==
!=
+=
-=
*=
/=
|=
&=
Ada
:=
=
/=
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
Operators in C and Ada (2)
Operator
Modulus
Remainder
Absolute Value
Exponentiation
Range
C/C++
%
Ada
mod
rem
abs
**
..
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
C/C++ types to Ada types
Declaring new types and subtypes
Simple types
Arrays
Records
Ada Types — outline
1
First View
2
Ada Types
C/C++ types to Ada types
Declaring new types and subtypes
Simple types
Arrays
Records
3
Ada Statements
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
C/C++ types to Ada types
Declaring new types and subtypes
Simple types
Arrays
Records
Declarations
Note that objects are defined in reverse order to C/C++,
the object name is first, then the object type.
As in C/C++ you can declare lists of objects by separating
them with commas.
C
int
int
int
int
Ada
i;
a, b, c;
j = 0;
k, l = 1;
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
i : Integer;
a, b, c : Integer;
j : Integer := 0;
k, l : Integer := 1;
Ada-95 dla programistów C/C++
First View
Types
Statements
C/C++ types to Ada types
Declaring new types and subtypes
Simple types
Arrays
Records
Constants
Another difference is in defining constants.
C
const int days_per_week = 7;
Ada
days_per_week : constant Integer := 7;
days_per_week : constant := 7;
In the Ada example it is possible to define a constant without
type, the compiler then chooses the most appropriate type to
represent it.
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
C/C++ types to Ada types
Declaring new types and subtypes
Simple types
Arrays
Records
Strong typing
Ada is a strongly typed language (possibly the strongest)
In C the use of typedef introduces a new name which
can be used as a new type.
The weak typing of C and even C++ (in comparison)
means that we have only really introduced a very poor
synonym.
C
Ada
typedef int INT;
INT a;
int b;
type INT is new Integer;
a : INT;
b : Integer;
a = b; //works
a := b; -- fails.
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
C/C++ types to Ada types
Declaring new types and subtypes
Simple types
Arrays
Records
Weaker typing
Strong typing can be a problem, and so Ada provides a feature
for reducing the distance between the new type and its parent.
subtype INT is Integer;
a : INT;
b : Integer;
a := b; -- works.
The most important feature of the subtype is to constrain the
parent type in some way, for example to place an upper or
lower boundary for an integer value.
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
C/C++ types to Ada types
Declaring new types and subtypes
Simple types
Arrays
Records
Integer types
Integer, Long_Integer etc.
Any Ada compiler must provide the Integer type,
this is a signed integer, and of implementation
defined size. The compiler is also at liberty to
provide Long_Integer, Short_Integer,
Long_Long_Integer etc. as needed.
Unsigned Integers
Ada does not have a defined unsigned integer, so
this can be synthesised by a range type, and
Ada-95 has a defined package,
System.Unsigned_Types which provide such a
set of types.
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
C/C++ types to Ada types
Declaring new types and subtypes
Simple types
Arrays
Records
Modular Integers
Ada-95 has added a modular type which specifies the
maximum value, and also the feature that arithmatic is cyclic,
underflow/overflow cannot occur.
type BYTE is mod 256;
type BYTE is mod 2**8;
Note: it is not required to use 2**x, you can use any value, so
10**10 is legal also.
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
C/C++ types to Ada types
Declaring new types and subtypes
Simple types
Arrays
Records
Characters and Boolean
Character
This is very similar to the C char type, and holds
the ASCII character set. However it is actually
defined in the package Standard as an
enumerated type. There is an Ada equivalent of
the C set of functions in ctype.h which is the
package Ada.Characters.Handling.
Ada Also defines a Wide_Character type for
handling non ASCII character sets.
Boolean
This is also defined in the package Standard as
an enumerated type (see below) as
(FALSE, TRUE).
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
C/C++ types to Ada types
Declaring new types and subtypes
Simple types
Arrays
Records
Strings (1)
Ada has a predefined String type (Standard).
There is a good set of Ada packages for string handling,
much better defined than the set provided by C.
Ada has a & operator for string concatenation.
Ada cannot use ’unconstrained’ types in static declarations.
type A_Record is
record
illegal : String;
legal
: String(1 .. 20);
end record;
procedure check(legal : in String);
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
C/C++ types to Ada types
Declaring new types and subtypes
Simple types
Arrays
Records
Strings (2)
The lower bound of the size must be greater than or equal
to 1.
The C/C++ array[4] which defines a range 0..3 cannot
be used in Ada, 1..4 must be used.
One way to specify the size is by initialisation, for example:
Name : String := "Simon";
is the same as defining Name as a String(1..5) and
assigning it the value "Simon" seperatly.
For parameter types unconstrained types are allowed,
similar to passing int array[] in C.
Ada has a package Ada.Strings.Unbounded which
implements a variable length string type.
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
C/C++ types to Ada types
Declaring new types and subtypes
Simple types
Arrays
Records
Floating point
Ada has two non-integer numeric types, the floating point
and fixed point types.
The predefined floating point type is Float and compilers
may add Long_Float, etc.
A new Float type may be defined in one of two ways:
type FloatingPoint1 is new Float;
type FloatingPoint2 is digits 5;
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
C/C++ types to Ada types
Declaring new types and subtypes
Simple types
Arrays
Records
Fixed point
Fixed point types are unusual, there is no predefined type
’Fixed’ and such type must be declared in the long form:
type Fixed is delta 0.1 range -1.0 .. 1.0;
This defines a type which ranges from -1.0 to 1.0 with an
accuracy of 0.1. Each element, accuracy, low-bound and
high-bound must be defined as a real number.
There is a specific form of fixed point types (added by
Ada-95) called decimal types. These add a clause
digits, and the range clause becomes optional.
type Decimal is delta 0.01 digits 10;
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
C/C++ types to Ada types
Declaring new types and subtypes
Simple types
Arrays
Records
Enumerations
Enumerations are true sets (not at all like C/C++s enums)
and the fact that the Boolean type is in fact:
type Boolean is (FALSE, TRUE);
should give you a feeling for the power of the type.
You have already seen a range in use (for strings), it is
expressed as low .. high and can be one of the most
useful ways of expressing interfaces and parameter values,
for example:
type Hours
is new Integer range 1 .. 12;
type Hours24 is range 0 .. 23;
type Minutes is range 1 .. 60;
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
C/C++ types to Ada types
Declaring new types and subtypes
Simple types
Arrays
Records
Subtypes for ranges
Another definition for Hours:
type Hours24 is new range 0 .. 23;
subtype Hours is Hours24 range 1 .. 12;
A subtype cannot extend the range beyond its parent, so
range 0 .. 25 would have been illegal.
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
C/C++ types to Ada types
Declaring new types and subtypes
Simple types
Arrays
Records
Combining enumerations and ranges (1)
type All_Days is (Monday, Tuesday, Wednesday,
Thursday, Friday, Saturday, Sunday);
subtype Week_Days is All_Days
range Monday .. Friday;
subtype Weekend is All_Days range
Saturday .. Sunday;
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
C/C++ types to Ada types
Declaring new types and subtypes
Simple types
Arrays
Records
Combining enumerations and ranges (2)
We can now take a Day, and see if we want to go to work:
Day : All_Days := Today;
if Day in Week_Days then
go_to_work;
end if;
Or you could use the form
if Day in range Monday .. Friday and we would not
need the extra types.
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
C/C++ types to Ada types
Declaring new types and subtypes
Simple types
Arrays
Records
Enumeration type handling (1)
Ada provides four useful attributes for enumeration type
handling:
Succ — this attribute supplies the ’successor’ to the
current value, so the ’Succ value of an object
containing Monday is Tuesday.
Note: If the value of the object is Sunday then an
exception is raised, you cannot Succ past the end
of the enumeration.
Pred — this attribute provides the ’predecessor’ of a
given value, so the ’Pred value of an object
containing Tuesday is Monday.
Note: the rule above still applies ’Pred of
Monday is an error.
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
C/C++ types to Ada types
Declaring new types and subtypes
Simple types
Arrays
Records
Enumeration type handling (2)
Val — this gives you the value (as a member of the
enumeration) of element n in the enumeration.
Thus Val(2) is Wednesday.
Note: the rule above still applies, and note also
that ’Val(0) is the same as ’First.
Pos — this gives you the position in the enumeration of
the given element name. Thus
’Pos(Wednesday) is 2.
Note: the range rules still apply, also that ’Last
will work, and return Sunday.
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
C/C++ types to Ada types
Declaring new types and subtypes
Simple types
Arrays
Records
Enumeration type handling (3)
All_Days’Succ(Monday) = Tuesday
All_Days’Pred(Tuesday) = Monday
All_Days’Val(0) = Monday
All_Days’First = Monday
All_Days’Val(2) = Wednesday
All_Days’Last = Sunday
All_Days’Succ(All_Days’Pred(Tuesday)) =
Tuesday
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
C/C++ types to Ada types
Declaring new types and subtypes
Simple types
Arrays
Records
Enumeration type handling (4)
Ada also provides a set of 4 attributes for range types, these
are intimately associated with those above and are:
First — this provides the value of the first item in a
range. Considering the range 0 .. 100 then
’First will obviously be 0.
Last — this provides the value of the last item in a
range, and so considering above, ’Last is 100.
Length — this provides the number of items in a range, so
’Length is actually 101.
Range — this funnily enough returns in this case the
value we gave it, but you will see when we come
onto arrays how useful this feature is.
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
C/C++ types to Ada types
Declaring new types and subtypes
Simple types
Arrays
Records
Arrays
Arrays in Ada make use of the range syntax to define their
bounds.
Arrays can be of any type.
Arrays can even be declared as unknown size.
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
C/C++ types to Ada types
Declaring new types and subtypes
Simple types
Arrays
Records
Some example (C)
char name[31];
int track[3];
int dbla[3][10];
int init[3] = { 0, 1, 2 };
typedef char[31] name_type;
track[2] = 1;
dbla[0][3] = 2;
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
C/C++ types to Ada types
Declaring new types and subtypes
Simple types
Arrays
Records
Some example (Ada)
Name
Name
Track
DblA
:
:
:
:
array (0 .. 30) of Character; -- OR
String (1 .. 30);
array (0 .. 2) of Integer;
array (0 .. 2) of array (0 .. 9) of
Integer; -- OR
DblA : array (0 .. 2,0 .. 9) of Integer;
Init : array (0 .. 2) of Integer := (0, 1, 2);
type Name_Type is array (0 .. 30) of Character;
track(2) := 1;
dbla(0,3) := 2;
-- Note try this in C.
a, b : Name_Type;
a := b; -- will copy all elements of b into a.
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
C/C++ types to Ada types
Declaring new types and subtypes
Simple types
Arrays
Records
Indexes (1)
non-zero based ranges
Because Ada uses ranges to specify the bounds
of an array then you can easily set the lower
bound to anything you want, for example:
Example : array (-10 .. 10) of Integer;
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
C/C++ types to Ada types
Declaring new types and subtypes
Simple types
Arrays
Records
Indexes (2)
non-integer ranges
The ranges above are all integer ranges, and so
we did not need to use the correct form which is:
array(type range low .. high)
which would make Example above
array(Integer range -10 .. 10). Now
you can see where we’re going, take an
enumerated type, All_Days and you can define
an array:
Hours_Worked : array (All_Days
range Monday .. Friday);
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
C/C++ types to Ada types
Declaring new types and subtypes
Simple types
Arrays
Records
Unbounded array types (1)
One of Ada’s goals is reuse, and to have to define a function to
deal with a 1..10 array, and another for a 0..1000 array is silly.
Therefore Ada allows you to define unbounded array types. An
unbounded type can be used as a parameter type, but you
cannot simply define a variable of such a type.
type Vector is array (Integer range <>)
of Float;
procedure sort_vector
(sort_this : in out Vector);
Illegal_Variable : Vector;
Legal_Variable
: Vector(1..5);
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
C/C++ types to Ada types
Declaring new types and subtypes
Simple types
Arrays
Records
Unbounded array types (2)
subtype SmallVector is Vector(0..1);
Another_Legal
: SmallVector;
This does allow us great flexibility to define functions and
procedures to work on arrays regardless of their size, so a call
to sort_vector could take the Legal_Variable object or
an object of type SmallVector, etc.
Note that a variable of type Smallvector is constrained and
so can be legally created.
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
C/C++ types to Ada types
Declaring new types and subtypes
Simple types
Arrays
Records
Array range attributes
If you are passed a type which is an unbounded array then if
you want to loop through it then you need to know where it
starts. So we can use the range attributes:
Example : array (1 .. 10) of Integer;
for i in Example’First .. Example’Last loop
for i in Example’Range loop
Note that if you have a multiple dimension array then the above
notation implies that the returned values are for the first
dimension, use the notation
Array_Name(dimension)’attribute
for multi-dimensional arrays.
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
C/C++ types to Ada types
Declaring new types and subtypes
Simple types
Arrays
Records
Initialisation by range (Aggregates)
When initialising an array one can initialise a range of elements
in one go:
Init : array (0 .. 3) of
Integer := (0 .. 3 => 1);
Init : array (0 .. 3) of
Integer := (0 => 1, others => 0);
The keyword others sets any elements not explicitly handled.
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
C/C++ types to Ada types
Declaring new types and subtypes
Simple types
Arrays
Records
Slicing (1)
Array slicing is something usually done with memcpy in C/C++.
Take a section out of one array and assign it into another.
Large : array (0 .. 100) of Integer;
Small : array (0 .. 3) of Integer;
-- extract section from one array
-- into another.
Small(0 .. 3) := Large(10 .. 13);
-- swap top and bottom halfs of an array.
Large := Large(51 .. 100) & Large(1..50);
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
C/C++ types to Ada types
Declaring new types and subtypes
Simple types
Arrays
Records
Slicing (2)
Note: Both sides of the assignment must be of the same type,
that is the same dimensions with each element the same. The
following is illegal.
-- extract section from one array into another.
Small(0 .. 3) := Large(10 .. 33);
-^^^^^^^^ range too big.
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
C/C++ types to Ada types
Declaring new types and subtypes
Simple types
Arrays
Records
Records
struct _device {
int
major_number;
int
minor_number;
char name[20];
};
typedef struct _device Device;
type struct_device
record
major_number :
minor_number :
name
:
end record;
type Device is new
is
Integer;
Integer;
String(1 .. 19);
struct_device;
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
C/C++ types to Ada types
Declaring new types and subtypes
Simple types
Arrays
Records
Initialization of members (1)
Device lp1 = {1, 2, "lp1"};
lp1 : Device := (1, 2, "lp1");
lp2 : Device := (major_number =>
minor_number =>
name
=>
tmp : Device := (major_number =>
name
=>
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
1,
3,
"lp2");
255,
"tmp");
Ada-95 dla programistów C/C++
First View
Types
Statements
C/C++ types to Ada types
Declaring new types and subtypes
Simple types
Arrays
Records
Initialization of members (2)
When initialising a record we use an aggregate, a construct
which groups together the members. This facility (unlike
aggregates in C) can also be used to assign members at other
times as well.
tmp : Device;
-- some processing
tmp := (major_number => 255, name => "tmp");
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
C/C++ types to Ada types
Declaring new types and subtypes
Simple types
Arrays
Records
Default values for record members
type struct_device is
record
major_number : Integer
minor_number : Integer
name : String(1 .. 19)
end record;
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
:= 0;
:= 0;
:= "unknown";
Ada-95 dla programistów C/C++
First View
Types
Statements
Compound Statement
if Statement
switch Statement
Ada loops
Ada Statements — outline
1
First View
2
Ada Types
3
Ada Statements
C/C++ statements to Ada
Compound Statement
if Statement
switch Statement
Ada loops
return
labels and goto
exception handling
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
Compound Statement
if Statement
switch Statement
Ada loops
Compound statement
A compound statement is also known as a block and in C
allows you to define variables local to that block, in C++
variables can be defined anywhere. In Ada they must be
declared as part of the block, but must appear in the declare
part just before the block starts.
C
Ada
{
declarations
statements
}
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
declare
declarations
begin
statement
end;
Ada-95 dla programistów C/C++
First View
Types
Statements
Compound Statement
if Statement
switch Statement
Ada loops
IF statement
If statements are the primary selection tool available to
programmers. The Ada if statement also has the ’elsif’
construct (which can be used more than once in any if
statement), very useful for large complex selections where a
switch/case statement is not possible.
C
Ada
if (expression)
{
statement
} else {
statement
}
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
if expression then
statement
elsif expression then
statement
else
statement
end if;
Ada-95 dla programistów C/C++
First View
Types
Statements
Compound Statement
if Statement
switch Statement
Ada loops
SWITCH statement
The switch or case statement is a very useful tool where the
number of possible values is large, and the selection
expression is of a constant scalar type.
C
Ada
switch (expression)
{
case value: statement
default:
statement
}
case expression is
when value => statement
when others => statement
end case;
There is a point worth noting here. In C the end of the
statement block between case statements is a break statement,
otherwise we drop through into the next case. In Ada this does
not happen, the end of the statement is the next case.
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
Compound Statement
if Statement
switch Statement
Ada loops
Ranges of values in SWITCH statement
C
Ada
switch (value) {
case 1:
case 2:
case 3:
case 4:
value_ok = 1;
break;
case 5:
case 6:
case 7:
break;
}
case value is
when 1..4 => value_ok := 1;
when 5 | 6 | 7 => null;
end case;
You will also note that in Ada thereAda-95
must
be a statement
for
dla programistów
C/C++
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
First View
Types
Statements
Compound Statement
if Statement
switch Statement
Ada loops
Loops
All Ada loops are built around the simple loop ... end
construct
loop
statement
end loop;
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
Compound Statement
if Statement
switch Statement
Ada loops
while Loop
The while loop is common in code and has a very direct Ada
equivalent.
while (expression)
{
statement
}
while expression loop
statement
end loop;
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
Compound Statement
if Statement
switch Statement
Ada loops
do Loop
The do loop has no direct Ada equivalent, though section
1.2.4.5 will show you how to synthesize one.
do
{
statement
} while (expression)
-- no direct Ada equivalent.
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
Compound Statement
if Statement
switch Statement
Ada loops
for Loop(1)
The for loop is another favourite, Ada has no direct equivalent
to the C/C++ for loop (the most frighteningly overloaded
statement in almost any language) but does allow you to iterate
over a range, allowing you access to the most common usage
of the for loop, iterating over an array.
for (init-statement ; expression-1 ;
loop-statement){
statement
}
for ident in range loop
statement
end loop;
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
Compound Statement
if Statement
switch Statement
Ada loops
for Loop (2)
Ada adds some nice touches to this simple statement:
the variable ident is actually declared by its appearance in
the loop, it is a new variable which exists for the scope of
the loop only and takes the correct type according to the
specified range.
to loop for 1 to 10 you can write the following Ada code:
for i in 1 .. 10 loop
null;
end loop;
to loop for 10 to 1 you must write the following Ada code:
for i in reverse 1 .. 10 loop
null;
end loop;
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
Compound Statement
if Statement
switch Statement
Ada loops
break and continue (1)
In C and C++ we have two useful statements break and
continue which may be used to add fine control to loops.
Consider the following C code:
while (expression) {
if (expression1) {
continue;
}
if (expression2) {
break;
}
}
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
Compound Statement
if Statement
switch Statement
Ada loops
break and continue (2)
In Ada there is no continue, and break is now exit.
while expression loop
if expression2 then
exit;
end if;
end loop;
The Ada exit statement however can combine the expression
used to decide that it is required, and so the code below is
often found.
while expression loop
exit when expression2;
end loop;
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
Compound Statement
if Statement
switch Statement
Ada loops
break and continue (3)
This leads us onto the do loop, which can now be coded as:
loop
statement
exit when expression;
end loop;
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
Compound Statement
if Statement
switch Statement
Ada loops
break and continue (4)
Another useful feature which C and C++ lack is the ability to
’break’ out of nested loops, consider
while ( (!feof(file_handle) &&
(!percent_found
)
) {
for (char_index = 0;
buffer[char_index] != ’\n’;
char_index++) {
if (buffer[char_index] == ’%’) {
percent_found = 1;
break;
}
// some other code,
// including get next line.
}
}
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
First View
Types
Statements
Compound Statement
if Statement
switch Statement
Ada loops
break and continue (5)
This sort of code is quite common, an inner loop spots the
termination condition and has to signal this back to the outer
loop. Now consider
Main_Loop:
while not End_Of_File(File_Handle) loop
for Char_Index in Buffer’Range loop
exit when Buffer(Char_Index) = NEW_LINE;
exit Main_Loop when
Buffer(Char_Index) = PERCENT;
end loop;
end loop Main_Loop;
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
Declarations and definitions
Functions and Procedures
Parameters
Part II
Sub-programs
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
Declarations and definitions
Functions and Procedures
Parameters
Outline
4
Declarations and definitions
5
Functions and Procedures
6
Parameters
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
Declarations and definitions
Functions and Procedures
Parameters
Declarations and definitions of sub-programs
The following piece of code shows how C/C++ and Ada both
declare and define a function. Declaration is the process of
telling everyone that the function exists and what its type and
parameters are. The definitions are where you actually write
out the function itself. (In Ada terms the function spec and
function body).
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
Declarations and definitions
Functions and Procedures
Parameters
Declarations and definitions of sub-programs in C
return_type func_name(parameters);
return_type func_name(parameters)
{
declarations
statement
}
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
Declarations and definitions
Functions and Procedures
Parameters
Declarations and definitions of sub-programs in Ada
function func_name(parameters) return return_type;
function func_name(parameters) return return_type is
declarations
begin
statement
end func_name
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
Declarations and definitions
Functions and Procedures
Parameters
RETURN Statement
Here again a direct Ada equivalent, you want to return a value,
then return a value,
return value; // C/C++ return
return value; -- Ada return
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
Declarations and definitions
Functions and Procedures
Parameters
Procedures
Let us now consider a special kind of function, one which does
not return a value. In C/C++ this is represented as a return type
of void:
void func_name(parameters);
In Ada this is called a procedure:
procedure func_name(parameters);
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
Declarations and definitions
Functions and Procedures
Parameters
Passing arguments
C/C++:
void func1(int by_value);
void func2(int* by_address);
void func3(int& by_reference); // C++ only.
Ada:
type int
is new Integer;
type int_star is access int;
procedure func1(by_value
: in
int);
procedure func2(by_address
: in out int_star);
procedure func3(by_reference : in out int);
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
Declarations and definitions
Functions and Procedures
Parameters
Sub-programs without arguments
void func_name();
void func_name(void);
int func_name(void);
procedure func_name;
function func_name return Integer;
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
Declarations and definitions
Functions and Procedures
Parameters
Parameter passing modes
Ada provides two optional keywords to specify how parameters
are passed, in and out. These are used like this:
procedure
procedure
procedure
procedure
proc(Parameter
proc(Parameter
proc(Parameter
proc(Parameter
: in
Integer);
:
out Integer);
: in out Integer);
:
Integer);
If these keywords are used then the compiler can protect you
even more, so if you have an out parameter it will warn you if
you use it before it has been set, also it will warn you if you
assign to an in parameter.
Note that you cannot mark parameters with out in functions as
functions are used to return values, such side affects are
disallowed.
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++
Declarations and definitions
Functions and Procedures
Parameters
Default parameters
Ada (and C++) allow you to declare default values for
parameters, this means that when you call the function you can
leave such a parameter off the call as the compiler knows what
value to use.
procedure
(File :
Mode :
Name :
Form :
Create
in out
in
in
in
File_Type;
File_Mode := Inout_File;
String
:= "";
String
:= "");
Create(File_Handle, Inout_File, "text.file");
Create(File => File_Handle,
Name => "text.file");
Dariusz Wawrzyniak (na podst. oprac. Simona Johnstona)
Ada-95 dla programistów C/C++